The present invention relates generally to an apparatus and method for automatically zeroing an output and, more particularly, to an automatic output zero for an exhaust emission analyzer and a method of use.
The presently known exhaust emission analyzers include a probe which is inserted into the exhaust pipe of the automobile to be tested. Once the probe is inserted, the pollution analyzer generates a pollution-indicating voltage which produces an output meter deflection, indicating the level of pollution in the exhausted air.
In many instances, the generated pollution-indicating voltage is inaccurate. For various reasons, such as the accumulation of dirt and dust particles in the optical path and aging of the infrared source of the analyzer, the generated pollution-indicating voltage can include a "free air" component, representing the voltage generated by the analyzer during analysis of open environmental air, i.e., with the probe exposed to clean atmospheric air. As such, the generated pollution-indicating voltage represents the sum of the true pollution-indicating voltage and free air voltage. The result is an erroneous pollution level indication.
The presently known analyzers include a potentiometer which is adjusted by the operator to zero the output meter just prior to the pollution test. The requirement of a manual adjustment, however, directly introduces human error into the compensating or zeroing process. Clearly, if the meter is not properly adjusted, the indicated pollution level remains inaccurate.